Electronic gearshift apparatus of sub gearshift for 4 wheel drive vehicle

ABSTRACT

An electronic gearshift device of a transfer case assembly for a four wheel drive vehicle is provided. The electric gearshift device comprises a motor, a camshaft rotatably driven by the motor, a rail member separated from the camshaft by a predetermined distance and positioned parallel to the camshaft; first and second forks installed on the rail member such that they are spaced apart from each other, and a cam fitted around and supported by the camshaft to selectively operate the first or second forks on the rail member to thereby effect gearshift.

TECHNICAL FIELD

The present invention relates, in general, to an electronic gearshiftdevice of a transfer case assembly for a four wheel drive vehicle, and,more particularly, to an electronic gearshift device of a transfer caseassembly for a four wheel drive vehicle, which employs a motor tocontrol operation of the transfer case assembly, thereby enablingautomatic gearshift.

BACKGROUND ART

As well known to those skilled in the art, transfer case assemblies fora four wheel drive vehicle are divided into a manual type in whichdriving scheme conversion is effected through manipulation of a driverand an electronic type in which driving mode conversion is effected byan electronic signal. In the manual type transfer case assembly, drivingscheme conversion of the four wheel drive vehicle is effected as thedriver directly manipulates a shift lever disposed adjacent to thedriver's seat.

The manual type transfer case assembly is encountered with a problem inthat, since the driver should directly manipulate the shift lever, thedriver can feel fatigued, it is bothersome to manipulate the shiftlever, and an accident is likely to occur while manipulating the shiftlever.

In these considerations, in these days, the electronic type transfercase assembly has been widely used throughout the world in that, sincegearshift is automatically effected, manipulation can be conducted in aconvenient manner, fatigue of the driver can be reduced, and it ispossible to prevent an accident from occurring.

A typical example of the conventional electronically controlled transfercase assembly is shown in FIG. 1.

A gearshift device 100 of the electronically controlled transfer caseassembly largely comprises a camshaft 102 which is rotated by a motor101 and is defined with a groove 103, a first fork 104 which functionsto convert a wheel driving scheme between a four wheel driving schemeand a two wheel driving scheme, a second fork 105 which is manuallyoperated by a separate lever (not shown) to convert a four wheel drivingmode between a four wheel high speed driving mode and a four wheel lowspeed driving mode, and a gearshift rod 106 having one end which iscoupled to the first fork 104 and the other end which is inserted andguided in the groove 103.

In the gearshift device 100 constructed as mentioned above, if thecamshaft 102 is rotated as power is applied to the motor 101, thegearshift rod 106 inserted in the groove 103 is moved along the groove103 to be changed in its position relative to the camshaft 102. As aresult of this, the first fork 104 to which the gearshift rod 106 iscoupled is moved to force a sleeve (not shown) to move, by whichconversion between the four wheel driving scheme and the two wheeldriving scheme is effected.

Consequently, as the motor 101 is rotated in forward or backwarddirections, gearshift is implemented into the four wheel driving schemeor the two wheel driving scheme.

In the meanwhile, with the wheel driving scheme converted into the fourwheel driving scheme by the first fork 104, when it is necessary toconvert the four wheel driving mode between the four wheel high speeddriving mode and the four wheel low speed driving mode, the position ofthe second fork 105 is moved by operating the separate lever, by whichthe four wheel driving mode can be converted from the four wheel highspeed driving mode into the four wheel low speed driving mode, and viceversa.

However, the conventional gearshift device 100 suffers from defects inthat, since the groove 103 should be defined with a high precision inthe camshaft 102, it is difficult to properly define the groove 103.Further, due to the fact that first gearshift means for effectingconversion of the wheel driving scheme between the four wheel drivingscheme and the two wheel driving scheme and second gearshift means foreffecting conversion of the four wheel driving mode between the fourwheel high speed driving mode and the four wheel low speed driving modeshould be separately provided, as the number of parts is increased, amanufacturing cost is increased, and inconvenience is caused due to theneed of operating the separate lever.

Also, referring to U.S. Pat. No. 6,155,126 describing another example ofa gearshift device for the electronically controlled transfer caseassembly, a shift fork body is slidably coupled to a shift rail. Whenthe shift rail is rotated, as the shift fork body is moved forward andbackward in an axial direction of the shift rail, a shift collar coupledto a web member is moved forward and backward to effect desiredgearshift.

Nevertheless, the conventional construction described just above has adrawback in that, since a cam for actually moving the shift fork bodyhas a configuration of a helical thread, its machining procedure iscomplicated. Moreover, the helical thread has a predetermined slope, itis impossible to implement gearshift in a diversity of ways.

Referring to U.S. Pat. No. 6,173,624 describing still another example ofa gearshift device for the electronically controlled transfer caseassembly, an inclined surface of a predetermined slope is formed on acam, and a cam follower is attached to an outer surface of a rail, sothat gearshift is effected as a camshaft is rotated.

Nonetheless, the conventional construction described just above is notfree from shortcomings in that, since the inclined surface of thepredetermined slope has a fixed contour, it is difficult to effectgearshift in a diversity of ways. In particular, because the camfollower, that is, a projection is formed on the outer surface of therail, a machining procedure is complicated, and inconvenience resultsfrom the need of changing a configuration of the entire rail.

In addition, because a fork is returned using one spring, it isdifficult to promptly and precisely return the fork into its originalposition.

DISCLOSURE OF THE INVENTION

Accordingly, the present invention has been made keeping in mind theabove problems occurring in the prior art, and an object of the presentinvention is to provide an electronic gearshift device of a transfercase assembly for a four wheel drive vehicle, which is constructed sothat gearshift means for effecting conversion between a four wheeldriving scheme and a two wheel driving scheme and gearshift means foreffecting conversion between a four wheel high speed driving mode and afour wheel low speed driving mode are integrated with each other,whereby the number of parts is decreased, a manufacturing cost isreduced, a driver's operational convenience is improved, fatigue of thedriver is reduced, it is possible to prevent an accident from occurring,and gearshift can be effected in a diversity of ways.

In order to achieve the above object, according to one aspect of thepresent invention, there is provided an electronic gearshift device of atransfer case assembly for a four wheel drive vehicle, comprising: amotor; a camshaft rotatably driven by the motor; a rail member separatedfrom the camshaft by a predetermined distance and positioned parallel tothe camshaft; first and second forks installed on the rail member suchthat they are spaced apart from each other; and a cam fitted around andsupported by the camshaft to selectively operate the first or secondforks on the rail member to thereby effect gearshift.

According to another aspect of the present invention, the cam is formedwith first and second operating sections for operating the first fork toeffect conversion between a four wheel driving scheme and a two wheeldriving scheme, and third and fourth operating sections for operatingthe second fork to effect conversion between a four wheel high speeddriving mode and a four wheel low speed driving mode.

According to another aspect of the present invention, in the cam, thefirst operating section comprises a flattened surface, the secondoperating section comprises a concaved surface having a predeterminedradius of curvature, and each of the third and fourth operating sectionscomprises a plane.

According to another aspect of the present invention, first and secondsprings for elastically supporting the first and second forks,respectively, are provided on the rail member.

According to still another aspect of the present invention, adjacent toa lower end of the first fork, a plunger which is elastically supportedby a compression spring is installed on a side of the first fork suchthat the plunger is selectively biased by the first or second operatingsections as the cam is rotated.

According to yet still another aspect of the present invention, a pinroller is installed on a side of the second fork such that the pinroller is selectively biased by the third or fourth operating sectionsas the cam is rotated.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description when taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a schematic cross-sectional view illustrating the conventionalelectronically controlled transfer case assembly;

FIG. 2 is a cross-sectional view illustrating an electronicallycontrolled transfer case assembly in accordance with a preferredembodiment of the present invention;

FIGS. 3 and 4 are perspective views independently illustrating a cam ofthe electronically controlled transfer case assembly according to thepresent invention; and

FIGS. 5 through 7 are cross-sectional views illustrating operationalstates of the electronically controlled transfer case assembly accordingto the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Reference will now be made in greater detail to a preferred embodimentof the invention, an example of which is illustrated in the accompanyingdrawings. Wherever possible, the same reference numerals will be usedthroughout the drawings and the description to refer to the same or likeparts.

FIG. 2 is a cross-sectional view illustrating an electronicallycontrolled transfer case assembly in accordance with a preferredembodiment of the present invention; FIGS. 3 and 4 are perspective viewsindependently illustrating a cam of the electronically controlledtransfer case assembly according to the present invention; and FIGS. 5through 7 are cross-sectional views illustrating operational states ofthe electronically controlled transfer case assembly according to thepresent invention.

An electronic gearshift device 10 of a transfer case assembly for a fourwheel drive vehicle in accordance with a preferred embodiment of thepresent invention comprises a motor 11, and a camshaft 12 which isrotatably driven by the motor 11.

A rail member 28 is separated from the camshaft 12 by a predetermineddistance and positioned above and parallel to the camshaft 12. First andsecond forks 21 and 25 are installed on the rail member 28 such thatthey are spaced apart from each other.

First and second springs 24 and 27 for elastically supporting the firstand second forks 21 and 25, respectively, are provided on the railmember 28.

Further, as characterizing features of the present invention, a cam 13is fitted around and supported by the camshaft 12 to selectively operatethe first or second forks 21 and 25 on the rail member 28 when thecamshaft 12 is driven by the motor 11, to thereby effect gearshift.

Describing a detailed structure of the cam 13, as shown in FIGS. 3 and4, the cam 13 is formed, at one end thereof with first and secondoperating sections 14 and 15 for operating the first fork 21 to effectconversion between a four wheel driving scheme and a two wheel drivingscheme.

Also, the cam 13 is formed, at the other end thereof with third andfourth operating sections 16 and 17 for operating the second fork 25 toeffect conversion between a four wheel high speed driving mode and afour wheel low speed driving mode.

At this time, describing detailed contour of the first through fourthoperating sections 14, 15, 16 and 17, the first operating section 14comprises a flattened surface, the second operating section 15 comprisesa concaved surface having a predetermined radius of curvature, and eachof the third and fourth operating sections 16 and 17 formed on the otherend of the cam 13 comprises a plane.

Meanwhile, a plunger 22 is installed on a side of the first fork 21adjacent to a lower end of the first fork 21. The plunger 22 iselastically supported by a compression spring 23 toward the cam 13 suchthat an end of the plunger 22 is elastically brought into contact withthe one end of the cam 13, that is, the first and second operatingsections 14 and 15 of the cam 13.

A pin roller 26 is installed on a side of the second fork 25 adjacent toa lower end of the second fork 25 such that an end of the pin roller 26is elastically brought into elastic contact with the other end of thecam 13, that is, the third and fourth operating sections 16 and 17 ofthe cam 13.

Hereafter, operations of the electronic gearshift device 10 of atransfer case assembly for a four wheel drive vehicle according to thepresent invention, constructed as mentioned above, will be described.

First, describing an operational state under a two wheel driving scheme,as power is applied to the motor 11, the camshaft 12 connected to arotation shaft of the motor 11 is rotatably driven.

As the camshaft 12 is rotated, the cam 13 which is fixedly fitted aroundthe camshaft 12 is rotated integrally with the camshaft 12, and at thesame time, the first and second forks 21 and 25 which are elasticallybrought into contact with the one and the other ends, respectively, ofthe cam 13 are rotated in an interlocked manner.

That is to say, in this state, the plunger 22 installed on the firstfork 21 is elastically brought into contact with the first operatingsection 14 of the cam 13 by the elastic force of the first spring 24,and the second fork 25 compresses the second spring 27 with the pinroller 26 brought into contact with the third operating section 16.

As can be readily seen from FIG. 2, in this state, the first and secondforks 21 and 25 are positioned left, by which the two wheel drivingscheme is effected.

If power is applied to the motor 11 to effect conversion from the twowheel driving scheme into the four wheel driving scheme, as the camshaft12 is rotated, the cam 13 is rotated integrally with the camshaft 12.With the rotation of the cam 13, the plunger 22 is moved from a firstportion 18 to a second section 19 and thereby compresses the compressionspring 23.

As the compression spring 23 is compressed in this way, the first fork21 is moved rightward while compressing the first spring 24.

Accordingly, while not shown in the drawings, a sleeve coupled to thefirst fork 21 is moved to effect conversion from the two wheel drivingscheme into the four wheel driving scheme.

At this time, even though the pin roller 26 is moved from the firstportion 18 to the second portion 19, since the second fork 25 is heldbrought into contact with the third operating section 16, that is, notchanged in its position, the four wheel driving scheme is maintained.

Then, when it is necessary to effect conversion from the four wheeldriving scheme into the two wheel driving scheme, as the camshaft 12 andthe cam 13 are reversely rotated using the motor 11, the plunger 22 andthe pin roller 26 are moved from the second portion 19 to the firstportion 18, as a result of which the force of the first fork 21,compressing the first spring 24, is removed and the first fork 21 isreturned to a leftward position by the elastic force of the first spring24 to effect the two wheel driving scheme.

Of course, even at this time, since the second fork 25 is held broughtinto contact with the third operating section 16, the two wheel drivingscheme is maintained.

In the meanwhile, with the first fork 21 operated to effect the fourwheel driving scheme, if it is necessary to convert a four wheel drivingmode from a four wheel high speed driving mode to a four wheel low speeddriving mode, the camshaft 12 and the cam 13 are further rotated in onedirection using the motor 11, so that the plunger 22 and the pin roller26 are moved to an endmost position of a third portion 20.

If the plunger 22 and the pin roller 26 are moved to the endmostposition of the third portion 20, the plunger 22 is still held in thesecond operating section 15, and the pin roller 26 is held in the fourthoperating section 17.

Therefore, while the first fork 21 is not changed in its position, thesecond fork 25 is moved rightward by the elastic force of the secondspring 27.

Hence, as a sleeve (not shown) coupled to the second fork 25 is moved,conversion is effected from the four wheel high speed driving mode tothe four wheel low speed driving mode. In the case that it is necessaryto effect conversion from the four wheel low speed driving mode to thefour wheel high speed driving mode, the cam 13 is reversely rotated toreturn the second fork 25 to its original position. In this way, thedesired conversion is accomplished.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

INDUSTRIAL APPLICABILITY

As apparent from the above description, the electronic gearshift deviceof a transfer case assembly for a four wheel drive vehicle according tothe present invention provides advantages in that gearshift means foreffecting conversion between a four wheel driving scheme and a two wheeldriving scheme and gearshift means for effecting conversion between afour wheel high speed driving mode and a four wheel low speed drivingmode are integrated with each other by the medium of a cam for operatingfirst and second forks. As a consequence, a driver can easily and stablyimplement gearshift while driving a car, safe driving is ensured, partscan be easily machined, the number of parts is decreased, and amanufacturing cost is reduced.

1. An electronic gearshift device of a transfer case assembly for a fourwheel drive vehicle, comprising: a motor; a camshaft rotatably driven bythe motor; a rail member separated from the camshaft by a predetermineddistance and positioned parallel to the camshaft; first and second forksinstalled on the rail member such that they are spaced apart from eachother; and a cam fitted around and supported by the camshaft toselectively operate the first or second forks on the rail member tothereby effect gearshift.
 2. The electronic gearshift device as setforth in claim 1, wherein the cam is formed with first and secondoperating sections for operating the first fork to effect conversionbetween a four wheel driving scheme and a two wheel driving scheme, andthird and fourth operating sections for operating the second fork toeffect conversion between a four wheel high speed driving mode and afour wheel low speed driving mode.
 3. The electronic gearshift device asset forth in claim 2, wherein, in the cam, the first operating sectioncomprises a flattened surface, the second operating section comprises aconcaved surface having a predetermined radius of curvature, and each ofthe third and fourth operating sections comprises a plane.
 4. Theelectronic gearshift device as set forth in claim 1, wherein first andsecond springs for elastically supporting the first and second forks,respectively, are provided on the rail member.
 5. The electronicgearshift device as set forth in claim 1, wherein, adjacent to a lowerend of the first fork, a plunger which is elastically supported by acompression spring is installed on a side of the first fork such thatthe plunger is selectively biased by the first or second operatingsections as the cam is rotated.
 6. The electronic gearshift device asset forth in claim 1, wherein a pin roller is installed on a side of thesecond fork such that the pin roller is selectively biased by the thirdor fourth operating sections as the cam is rotated.